Multi-zonal monofocal intraocular lens for correcting optical aberrations

ABSTRACT

A multi-zonal monofocal opthalmic lens comprises an inner zone, an intermediate zone, and an outer zone. The inner zone has a first optical power. The intermediate zone surrounds the inner zone and has a second optical power that is different from the first power by a magnitude that is less than at least about 0.75 Diopter. The outer zone surrounds the intermediate zone and has a third optical power different from the second optical power. In certain embodiments, the third optical power is equal to the first optical power.

RELATED APPLICATION

[0001] The present application claims priority under 35 U.S.C §119(e) toprovisional application No. 60/424,851, filed on Nov. 8, 2002 under thesame title. Full Paris Convention priority is hereby expressly reserved.

FIELD OF THE INVENTION

[0002] This invention relates to intraocular lenses (IOLs) and, moreparticularly, to multi-zonal monofocal IOLs that correct opticalaberrations for a variety of human eyes with different corneas under awide range of lighting conditions and that are effective even whendecentered or tilted.

BACKGROUND OF THE INVENTION

[0003] In the perfect eye, an incoming beam of light is focused throughthe cornea and through the crystalline lens in a way that causes all ofthe light from a point source to converge at the same spot on the retinaof the eye, ideally on the fovea area of the retina. This convergenceoccurs because all of the optical path lengths, for all light in thebeam, are equal to each other. Stated differently, in the perfect eyethe time for all light to transit through the eye will be the sameregardless of the particular path that is taken by the light.

[0004] Not all eyes, however, are perfect. The consequences of this arethat light path lengths through the eye become distorted and are not allequal to each other. Thus, light from a point source that transits animperfect eye will not necessarily come to the same spot on the retinaand be focused.

[0005] As light enters and passes through an eye it is refracted at theanterior surface of the cornea, at the posterior surface of the cornea,and at the anterior and posterior surfaces of the crystalline lens,finally reaching the retina. Any deviations that result in unequalchanges in these optical path lengths are indicative of imperfections inthe eye that may need to be corrected. For example, many people arenear-sighted because the axial length of their eyes are “too long”(myopia). As a result, the sharp image of an object is generated not onthe retina, but in front of or before the retina. Hyperopia is acondition where the error of refraction causes rays of light to bebrought to a focus behind the retina. This happens because the axiallength is “too short”. This condition is commonly referred to asfarsightedness. Another refractive malady is astigmatism resulting froma refractive surface with unequal curvatures in two meridians. Thedifferent curvatures cause different refractive powers, spreading lightin front and in back of the retina.

[0006] Other “higher order” maladies of interest for vision correctioninclude coma and spherical aberration. Coma exists when an asymmetry inthe optical system causes unequal optical path lengths in a preferreddirection. For example, the image of an off-axis point object takes on acomet-like shape. For symmetrical systems, spherical aberration existswhen rays at different radial heights from the optical axis focus atdifferent axial locations near the retina. Whereas coma exists only inasymmetric systems, spherical aberration can exist in both symmetric andasymmetric systems. Other, even higher order, aberrations exist.However, studies have show that spherical aberration is one of thestrongest higher order aberrations in the human visual system. Thus theretinal image may be improved if the spherical aberration is correctedaccording to known techniques.

[0007] Studies have also shown that there is a balance between thepositive spherical aberration of the cornea and the negative sphericalaberration of the crystalline lens in younger eyes. As one grows older,the spherical aberration of the crystalline lens becomes more positive,increasing the overall spherical aberration and reducing the imagequality at the retina.

[0008] An intraocular lens (IOL) is commonly used to replace the naturallens of a human eye when warranted by medical conditions such ascataracts. In cataract surgery, the surgeon removes the naturalcrystalline lens from the capsular bag or posterior capsule and replacesit with an IOL. IOLs may also be implanted in an eye (e.g., in theanterior chamber) with no cataract to supplement the refractive power ofthe natural crystalline lens, correcting large refractive errors.

[0009] The majority of ophthalmic lenses including IOLs are monofocal,or fixed focal length, lenses that primarily correct refractive error.Most monofocal IOLs are designed with spherical anterior and posteriorsurfaces. The spherical surfaces of the typically positive power IOLscause positive spherical aberration, inter alia. Thus, replacement ofthe crystalline lens with a typical monofocal IOL leaves the eye withpositive spherical aberration. In real eyes with complex cornealaberrations, the eye following cataract surgery is left a with finitenumber of complex lower and higher order aberrations, limiting the imagequality on the retina.

[0010] Some examples of attempts to measure higher order aberrations ofthe eye as an optical system in order to design an optical lens includeU.S. Pat. No. 5,062,702 to Bille, et al., U.S. Pat. No. 5,050,981 toRoffman, U.S. Pat. No. 5,777,719 to Williams, et al., and U.S. Pat. No.6,224,211 to Gordon.

[0011] A typical approach for improving the vision of a patient has beento first obtain measurements of the eye that relate to the topography ofthe anterior surface of the cornea. Specifically, the topographymeasurements yield a mathematical description of the anterior surface ofthe cornea. This corneal surface is placed in a theoretical model of thepatient's eye with an IOL replacing the crystalline lens. Ray-tracingtechniques are employed to find the IOL design which corrects for thespherical aberration of the cornea. Ideally, if implanted with thiscustom IOL, the patient's vision will improve.

[0012] Recently, Pharmacia Corp. (Groningen, Netherlands) introduced aposterior capsule intraocular lens having the trade name TECNIS (Z9000)brand of Silicone IOL. The TECNIS lens has a prolate anterior surface,which is intended to reduce spherical aberrations of the cornea. Thislens may be designed using methods described in U.S. Pat. No.

[0013] and PCT publication WO 01/89424, both to Norrby, et al. Themethods in these publications involve characterizing aberrant cornealsurfaces as linear combinations of Zernike polynomials, and thenmodeling or selecting an intraocular lens which, in combination with acharacteristic corneal surface, reduces the optical aberrations ocularsystem. The lenses resulting from these methods may be continuousaspherical surfaces across the entire optical zone and may be used toreduce spherical aberrations of the eye by introducing negativespherical aberration to counter the typically positive sphericalaberration of the cornea. In these lenses, there may be a single basecurve on which the aspheric surface is superimposed. As reported by J.T. Holliday, et al., “A New Intraocular Lens Designed to ReduceSpherical Aberration of Pseudophakic Eyes,” Journal of RefractiveSurgery 2002, 18:683-691, the Technics IOL has been found to be toimprove visual contrast sensitivity at a frequency up to 18cycles/degree.

[0014] The TECNIS brand of lens generally requires precise positioningin the capsular bag to provide improved optical quality over a sphericalIOL (c.f., “Prospective Randomized Trial of an Anterior Surface ModifiedProlate Intraocular Lens,” Journal of Refractive sugery, Vo. 18, Nov/Dec2002). Slight errors in decentration (radial translation) or tilt (axialrotation) greatly reduces the effectiveness of the lens, especially inlow-light conditions, thus making the task of the surgeon moredifficult. Furthermore, shrinkage of the capsular bag or otherpost-implantation anatomical changes can affect the alignment or tilt ofthe lens along the eye's optical axis. It is believed that the “typical”magnitude of decentration resulting from the implantation of anintraocular lens in an average case, and factoring in post-implantationmovement, is less than about 1.0 mm, and usually less than about 0.5 mm.Most doctors agree that decentration of an IOL greater than about 0.15to approximately 0.4 mm is clinically relevant (i.e., noticeably affectsthe performance of the optical system, according to those skilled in theart). Similarly, the “typical” magnitude of tilt resulting from theimplantation of an intraocular lens in an average case, and factoring inpost-implantation movement, is less than about 10 degrees, and usuallyless than about 5 degrees. Therefore, in practice, the benefits of theTECNIS brand of lens may be offset by its apparent drawbacks in the realworld.

[0015] In view of the above, there remains a need for an intraocularlens that corrects for spherical aberrations in a variety of lightingconditions and is less sensitive to non-optimal states such asdecentration and tilt of the IOL.

SUMMARY OF THE INVENTION

[0016] The present invention provides a multi-zonal monofocal ophthalmiclens that is less sensitive to its disposition in the eye by reducingaberrations, including the spherical aberration, over a range ofdecentration. The monofocal ophthalmic lenses of the present inventionmay also be configured to perform well across eyes with differentcorneal aberrations (e.g., different asphericities).

[0017] In one aspect of the invention, a multi-zonal monofocal opthalmiclens comprises an inner zone, an intermediate zone, and an outer zone.The inner zone has a first optical power. The intermediate zonesurrounds the inner zone and has a second optical power that isdifferent from the first power by a magnitude that is less than at leastabout 0.75 Diopter. The outer zone surrounds the intermediate zone andhas a third optical power different from the second optical power. Incertain embodiments, the third optical power is equal to the firstoptical power. The ophthalmic lens may comprise between 3 and 7 totalzones, but favorably comprises between 3 and 5 total zones. However,ophthalmic lenses with more than seven total zones are consistent withembodiments of the invention.

[0018] In another aspect of the invention, a multi-zonal monofocalintraocular lens has an optic with a plurality of concentric opticalzones centered on the optical axis. The zones are adapted to focusincoming light rays to form the image from one object. The intraocularlens optic includes an inner zone overlapping the optical axis of thelens that provides an image when the intraocular lens is centered on theoptical axis of the human eye. A first surrounding zone concentric aboutthe inner zone is adapted to compensate for optical aberrationsresulting from implanted intraocular lens decentration of greater thanat least about 0.1 mm.

[0019] The first surrounding zone may be configured to compensate foroptical aberrations resulting from implanted intraocular lensdecentration of greater than at least about 0.1 mm. The firstsurrounding zone may also compensate for optical aberrations resultingfrom implanted intraocular lens tilt of greater than at least about 1degree. The power of the first surrounding zone preferably differs fromthe power of the inner zone by a magnitude that is less than or equal toat least about 0.75 Diopter. In an exemplary embodiment, the inner zonecomprises a spherical surface and the first surrounding zone comprisesan aspherical surface.

[0020] Another aspect of the invention includes a method of designingmulti-zonal monofocal opthalmic lens. The method comprises providing anoptical model of the human eye. The method further comprises an opticalmodel of a lens comprising an inner zone, an intermediate zone, an outerzone, and zonal design parameters. The method also comprises adjustingthe zonal design parameters based on an image output parameter for oneor more non-optimal states of the lens.

[0021] The method may further include testing the intraocular lens overa wide range of clinically relevant corneal surface variations anddispositions of optical elements in the eye's optical system usingray-trace analysis techniques. Furthermore, the method may be repeatedto modify zonal parameters and achieve a better average opticalperformance. Examples of conditions of asymmetry that the lens willcorrect include decentration, tilt, and corneal aberrations.

[0022] The invention, together with additional features and advantagesthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying illustrativedrawings in which like parts bear like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a schematic vertical cross-section of the human eye in abright light environment and showing a pair of light rays passingthrough the optical system of the cornea and an implanted intraocularlens of the prior art to focus on the retina.

[0024]FIG. 2 is a schematic vertical cross-section of the human eye in alow light environment and showing a pair of light rays passing throughthe optical system of the cornea and the peripheral regions of animplanted intraocular lens of the prior art to focus in front of theretina.

[0025]FIG. 3 is a schematic vertical cross-section of the human eye in abright light environment and showing a pair of light rays passingthrough the optical system of the cornea and a decentered implantedintraocular lens of the prior art to focus on the retina.

[0026]FIG. 4 is a schematic vertical cross-section of the human eye in amedium light environment and showing a pair of light rays passingthrough the optical system of the cornea and a decentered implantedintraocular lens of the prior art to focus in front of the retina.

[0027]FIGS. 5A and 5B are schematic plan and side views of a monofocalintraocular lens of the present invention illustrating concentric zonesabout an optical axis.

[0028]FIGS. 6A and 6B show simulated modulation transfer functions foran aspheric, spherical and multi-zonal monofocal IOLs at a 5 mm pupildiameter with no decentration and 0.5 mm decentration, respectively.

[0029]FIG. 7 show simulated aspheric, spherical, and multi-zonalmonofocal IOL MTF curves at a 5 mm pupil diameter representing therespective average MTFs over 100 eyes varying in corneal aberrations,IOL decentration and tilt, and small pupil size changes.

DETAILED DESCRIPTION

[0030] The present invention encompasses an intraocular lens (IOL)design that reduces sensitivity to decentration within the eye whilemaintaining superior Module Transfer Function (MTF) performance forlarge pupils. The MTF is a measure of visual performance that can beplotted on a non-dimensional scale from a minimum of 0.0 to a maximum of1.0 cross a range of spatial frequencies in units of cycles per mm. TheMTF is a measure of the fficiency of “transferring” the contrast of anobject into an image. The spatial frequency is nversely proportional tothe size of the object. Thus, small objects at the limit of visualresolution have high spatial frequencies than larger objects. The IOLdescribed herein comprises a multi-zonal monofocal lens in which theanterior lens surface, posterior lens surface, or both comprises aplurality of zones that operate together on an incident wavefront toproduce a corrected ocular image. The different zones of the IOL of thepresent invention, as described in greater detail below herein,generally have different mean spherical curvatures and/or Diopterpowers, but the Diopter power differences between zones are far lessthan the typical 2 Diopter to 4 Diopter design differences associatedwith multi-focal IOLs. In certain embodiments, the maximum Diopter powerdifference between any two zones is less than at least about 0.75 D,advantageously less than about 0.65 D.

[0031] As used herein, the term “monofocal lens” is considered to be alens in which light entering the lens from a distant point source isfocused to substantially a single point. In the case of a multi-zonalmonofocal lens, light from a distant point source entering the lens.zones substantially fall within the range of the depth-of-focus of aspherical lens having an equivalent focal length.

[0032] As used herein in reference to the zones of a multi-zonalmonofocal lens, the terms “optical power” and “Diopter power” refer tothe effective optical or Diopter power of a zone when the lens is partof an ocular lens system such as, for example, a cornea, a multi-zonalmonofocal IOL, a retina, and the material surrounding these components.This definition may include the effects of the vergence or angle oflight rays intersecting the IOL surface caused by the power of thecornea. This may include the total vergence from all optical surfaces infront of the multi-zonal monofocal IOL. In certain instances, analgorithm for calculating the Diopter power may begin with a ray-tracinga model of the human eye incorporating a multi-zonal monofocal IOL. At aparticular radial location on the IOL surface, Snell's law may beapplied to calculate the angle of the light ray following therefraction. The optical path length of the distance between a point onthe surface and the optical axis (axis of symmetry) may be used todefine the local radius of curvature of the local wavefront. Using suchan approach, the Diopter power is equal to the difference in indicies ofrefraction divided by this local radius of curvature.

[0033] IOLs of the present invention are designed to outperform certainIOLs of the prior art in low or moderate light situations over a largerrange of implant positions. In practice, clinicians recognize that inthe average case intraocular lenses implanted in the posterior capsuleend up decentered from the optical axis of the host eye by between about0.15-0.4 mm. Sometimes the decentration is greater as a result of poorimplant technique or non-axisymmetric forces imparted by the host eye.Indeed, decentration of more than 0.5 mm, and sometimes up to 1.0 mm isexperienced. IOLs of the present invention are specifically designed toexhibit superior performance in comparison to the prior art IOLs whendecentered by at least about 0.15 mm and in particular in low ormoderate light conditions. In certain embodiments, IOLs of the presentinvention are designed to exhibit superior performance in comparison toprior art IOLs when decentered by greater than about 0.5 mm or greaterthan about 1.0 mm. The amount of decentering to be accommodated dependsupon design constraints such as, for example, the accuracy of thesurgical method to be used for implanting the IOL. Since the multi-zonalmonofocal IOLs provide improved performance for decentered conditions,it is anticipated that patients will generally experience greatersatisfaction with a multi-zonal monofocal IOL than with other prior artIOLs.

[0034]FIG. 1 is a schematic vertical cross-section through a human eye20 having an IOL 22 of the prior art implanted therein. The opticalsystem of the eye 20 includes an outer cornea 24, a pupil 26 defined byan orifice of an iris 28, the IOL 22, and a retina 30 formed on theposterior inner surface of the ocular globe 32. In the presentapplication, the terms anterior and posterior are used in theirconventional sense; anterior refers to the front side of the eye closerto the cornea, while posterior refers to the rear side closer to theretina. The eye defines a natural optical axis OA. The drawing shows theeye 20 in a bright light environment with the iris 28 constrictedresulting in a relatively small pupil 26.

[0035] The exemplary IOL 22 is adapted to be centered along the opticalaxis OA and within a capsular bag (not shown) just posterior to the iris28. For this purpose, the IOL 22 may be provided with haptics orfixation members 34. An optic of the IOL 22 is defined by an anteriorface 36 and posterior face 38. The optic may take a variety ofconfigurations known in the art, such as the convex-convex configurationillustrated in FIG. 5B. It should be understood that the presentinvention is not limited to posterior capsule-implanted IOLs.

[0036] A pair of light rays 40 pass through cornea 24, pupil 26, the IOL22. The rays 40 then focus on the retina 30 along the optical axis OA.In the bright light environment shown, the light rays 40 pass throughthe mid-portion of the lens optic. The intraocular lenses of the priorart are relatively effective in focusing such light rays at a point onthe retina 30 along the optical axis OA.

[0037]FIG. 2 shows the eye 20 having the IOL 22 therein in a low lightenvironment. In such situations, the iris 28 opens up creating arelatively large pupil 26 and permitting more light to strike the IOL22. A pair of light rays 42 passing through the peripheral regions ofthe pupil 26 may be incorrectly refracted by the peripheral regions ofthe optic of the IOL 22 in the manner shown. That is, the light rays 42focus on a spot 44 along the optical axis OA that is in front of theretina 30 by a distance 46. Such refraction is termed positive sphericalaberration because the light rays 42 focus in front of the retina 30. Anegative spherical aberration focuses light rays at the imaginary pointalong the optical axis OA behind the retina 30. Such aberrations canalso occur in an eye with the natural lens still in place. For example,the crystalline lens in the aging eye may not refract light properlyunder low light environments. The practical result of such a conditionmay be a loss in image quality.

[0038]FIG. 3 illustrates the human eye 20 in a bright light environmentsuch as shown in FIG. 1. The IOL 22 centered along the optical axis OAis again shown in solid line, but is also shown in dashed line 22′representing a condition of decentration. As mentioned above,decentration involves a radial translation of the intraocular lens froma centered configuration on the natural optical axis OA. The light rays40 pass through the cornea 24 and relatively small pupil 26, and arerefracted through the central region of the decentered intraocular lensoptic 22′. That is, despite the undesirable decentration, the optic 22′performs well in bright light environments because light does not strikeand refract through its peripheral regions.

[0039]FIG. 4 illustrates the eye 20 in a medium light environment, inwhich the iris 28 is somewhat larger compared to the condition shown inFIG. 3, but is not fully expanded as seen in the low light environmentof FIG. 2. Under such conditions, a centered IOL 22 would likely performadequately, but the decentered lens 22′ will not. More particularly, alight ray 48 passing close to the iris 28 will strike and be incorrectlyrefracted through a peripheral region of the decentered optic 22′ asshown. Intraocular lenses of the prior art have varying degrees ofsensitivity to decentration, and the situation shown in FIG. 4 is forillustration purposes only and does not represent any particular lens.

[0040] However, it is believed that certain lenses designed to correctfor spherical aberration, such as the TECNIS brand of lens, arerelatively sensitive to small magnitudes of decentration. Such lenseshave a complex refractive surface that changes relatively continuouslyacross whichever face it is formed (i.e., anterior or posterior). Thiscontinuous refractive surface provides a negative correction for thepositive spherical aberration on the cornea, but when the lens isdecentered the closely calculated balance between the two opticaldevices may be lost. Indeed, other optical aberrations such as coma andastigmatism may be created by the resulting mismatch.

[0041]FIGS. 5A and 5B schematically illustrate in plan and side views amonofocal IOL 60 of the present invention having an optic 62 and a pairof haptics or fixation members 64a, 64b extending outward therefrom. Theoptic 62 has a generally circular peripheral edge 66 and a plurality ofconcentric annular refractive bands or zones formed thereon. Theperipheral edge 66 is desirably an axially oriented edge with thickness,as seen in FIG. 5B, although curved or angled edge surfaces, orcombinations thereof, are possible. The optic 62 has an anterior face 68a and an opposite posterior face 68 b separated by the peripheral edge66. It should be understood that the refractive zones can be formed oneither the anterior or posterior face, or in some cases as a combinationof both faces. A central and inner zone 70 centered on the optical axisOA extends outward to a radius of r₁, at least one intermediate zone 72surrounds the inner zone 70 and extends outward to a radius of r₂, andan outer zone 74 surrounds the intermediate zone 72 and extendstherefrom to the outer periphery 66 of the optic 62 and a radius of r₃.Desirably, r₁ is between about 1-1.5 mm, r₂ is between about 1.5-2.2 mm,and r₃ is about 3 mm. More desirably, r₁ is about 1.4 mm and r₂ is about2.0 mm. In certain instances, it may be desirable that r₃ is greaterthan 3 mm, for instance in order to preclude undesired edge effects.

[0042] The inner zone 70, intermediate zone 72, and outer zone 74 mayhave surfaces that are either spherical or aspherical in shape. Theintermediate zone 72 may comprise a combination of annular zones,although a single annular zone is generally desirable. In certainembodiments, the inner zone 70 is spherical, the intermediate zone 72 isaspherical, and the outer zone 74 is also aspherical.

[0043] The power of the inner zone 70 dominates the visual performanceof the eye when the pupil is small, such as in bright daylightsituations. The intermediate zone 72 is at least designed to helpcorrect aberrations of the IOL when it is decentered, tilted, orotherwise in a non-optimal state. The power of intermediate zone 72 isextremely close to that of the inner zone 70. The outer zone 74 may beaspherical and designed to minimize the spherical aberrations natural tospherical monofocal IOLs.

[0044] Preferably, the intermediate zone 72 has a correction power thatis less than the correction power of the inner zone 70. When a prior artIOL is decentered (FIG. 4), peripheral light is too strongly refractedand focuses in front of the retina. However, the intermediate zone 72 ofthe multi-zonal monofocal IOL 60 is used to reduce surface power,redirecting the light ray 48 to the focal point on the retina. Theintermediate zone 72 may also provide correction in cases of tilting ofthe lens within the typical range of at least about 1 to 10 degrees,depending upon design constraints such as, for example, the accuracy ofthe surgical method to be used for implanting the IOL.

[0045] The IOL 60 is considered to be a monofocal lens because therelative refractive powers of the zones 70, 72, and 74 are close to oneanother and within the range of the depth-of-focus of typical sphericalmonofocal IOLs. In this context, a “monofocal” lens is one in, whichdiscrete adjacent regions or zones have a maximum difference inrefractive power of less than at least about 0.75 Diopter. Therefractive power of any one zone may be interpreted as the mean powerwithin that zone. It should also be understood that discrete adjacentzones does not necessarily mean that there is a sharp physicaltransition therebetween, rather the manufacturing process may bedesigned to generally provide a smooth transition between adjacentzones.

[0046] The IOL 60 may be fabricated from materials used in the art, suchas silicon, acrylic, or Polymethylmethacrylate (PMMA), or any othermaterial that is suitable for use in or on a human eye. Materials mayalso be selected so as to provide a desired optical performance. Forinstance, the refractive index is known to vary with different materialsand may, therefore, be used as a design parameter for attaining adesired optical performance or affect from the IOL 60.

[0047] The IOL 60 may also be used in conjunction with other opticaldevices such as diffractive optical elements (DOE). For example, theanterior lens surface of the IOL 60 may comprise a multi-zonal surfaceand the posterior lens surface may contain a DOE such as a diffractivegrating, or visa versa. Alternatively, the multi-zonal surface itselfmay comprise a DOE such as a diffractive grating. The DOE may also beused, for example, to correct for chromatic aberrations or to improvethe performance of the IOL 60 when displaced from the optimal position(e.g., centered and normal to the optical axis). In certain embodiments,the DOE is disposed over only a portion of the one of the IOL surfaces.For example, the DOE may be disposed over the intermediate zone 72 andused as an additional parameter for improving the performance of the IOL60.

[0048] The IOL 60 may be designed to have a nominal optical power suitedfor the particular environment in which it is to be used. It isanticipated that the nominal optical power of the IOL 60 will generallybe within a range of about −20 Diopters to at least about +35 Diopters.Desirably, the optical power of the IOL 60 is between about 10 Dioptersto at least about 30 Diopter. In certain applications, the optical powerof the IOL 60 is approximately 20 Diopters, which is a typical opticalpower for the natural crystalline lens in a human eye.

[0049] Under low light environments, such as night-time, the human eyehas a larger pupil (about 4.5-6 mm in diameter) and hence has a largespherical aberration (SA) that blurs the image. Clinically, thelarge-pupil eye is reported to have a lower contrast sensitivity andsometimes lower visual acuity. The TECNIS brand of lens has beenreported to perform better than spherical IOLs in low light environmentsas judged by visual contrast sensitivity and visual acuity. According tosimulations, however, this aspherical design is sensitive todecentration. A fraction of a millimeter decentration of such IOLs fromthe optical axis may dramatically break the balance of SA between IOLand cornea, and thus seriously degrade the eye's vision.

[0050] The inventors have discovered that spherical aberration can bereduced for both on-design and off-design conditions by forming a lenssurface to have a multi-zonal structure, with each zone having differentsurface parameters, for example, the base radius of curvature. Incontrast with the prior art single continuous aspheric surface, such asthe TECNIS brand of lens described above, the surface sag of the IOL 60(i.e. multi-zonal surface contour) may be determined using an equationthat changes across the lens. In accordance with an exemplary embodimentof the present invention, the surface sag at any radius from the opticalaxis for an ith zone is given by the following equation:${Sag} = {\frac{C_{i}*r^{2}}{1 + \sqrt{1 - {\left( {1 + K_{i}} \right)*C_{i}^{2}*r^{2}}}} + {\sum\limits_{j = 0}^{M}\quad {B_{i\quad j}*\left( {r - r_{i}} \right)^{2j}}} + {\sum\limits_{j = 1}^{M}\quad {T_{i\quad j}*\left( {r - r_{i - 1}} \right)^{2j}}}}$

[0051] where C_(i), K_(i), and r_(i) are the base radius of curvature,the asphericity constant, and the height of the ith zonal surface.Further, the Bjs and Tjs are optional boundary parameters that can beused to connect the zonal surfaces smoothly. The variable M is aninteger that determines how smoothly one zone transitions to another.This work makes use of a published finite eye model to represent the“nominal” eye for IOL design (see, Liou H. L. and Brennan N. A.,“Anatomically Accurate, Finite Model Eye for Optical Modeling, J Opt SocAm A, 1997; 14:1684-1695).

[0052] For posterior chamber IOL design, the asphericity constant K₁ inthe inner zone 70 (FIG. 5A) is preferably zero (i.e., the inner zone 70comprises a spherical surface). The base radius of curvature C₁ in theinner zone 70 is considered to be the base surface power of the lens.There are preferably at least three zones (i≧3) to achieve enhancedperformance for a 6 mm diameter pupil size. A preferred range of thenumber of zones is between at least about 3-7, more preferably between3-5; however, larger numbers of zones may be used of particular designconditions. The parameters in the outlying zones can be optimallydetermined such that each zonal surface refracts more of the light raysin that particular zone to the focus set by the inner zone. This processcan be achieved by the aid of a commercial optical ray tracing designsoftware, such as ZEMAX optical design program from ZEMAX DevelopmentCorporation (4901 Morena Blvd. Suite 207, San Diego, Calif. 92117-7320).

[0053] In general, the base curves in at least two zones are different(preferably the inner and intermediate zones), though all zones may havedifferent base curves. Desirably, the anterior surface has three zones,each having a different base radius of curvature. The posterior surfaceis a one zone spherical surface.

[0054] Table 1 provides an example of a multi-zonal monofocal IOLconsistent with the present invention. The values of the parametersgiven below are for an IOL with an overall Diopter power of 20 having 3zones (i=3) on the anterior surface and one zone on the posterior (i=1).TABLE I Surface parameters of a 20D multi-zonal structured IOL Symbol i= 1 i = 2 i = 3 Anterior surface parameter Zonal outer radial r_(i) (mm)1.414 2.000 3.000 boundary, mm Zonal curvature of C_(i) 0.086149000000.0751110000000 0.05055500000000 radius, 1/mm (1/mm) Zonal asphericityK_(i) 0.00000000000000 −1.5931120000000 8.90504900000000 M = 3 B_(i0)0.00163052185449 0.01542174622418 0.11151991935001 B_(i1)−0.0024465216312 −0.0241315485668 −0.0611825408097 B_(i2)0.00122363035200 0.08421200000000 0.00963200000000 B_(i3)−0.0002040000000 −0.1293190000000 0.00399800000000 T_(i1)0.00000000000000 .02774300000000 −0.0571790000000 T_(i2)−0.0004750000000 −0.1375720000000 0.13027200000000 T_(i3)0.00007700000000 0.23032800000000 −0.0800460000000 Posterior surfaceparameter Zonal outer radial r_(i) (mm) 3.000 boundary, mm Zonalcurvature of C_(i) 0.0636027120000 radius, 1/mm (1/mm) Zonal asphericityK_(i) 0.00000000000000 M = 0 N/A

[0055]FIGS. 6A and 6B illustrate the IOL performance the multi-zonalmonofocal lens shown in Table 1 in terms of the simulated modulationtransfer functions as compared to both a spherical lens and an asphericlens (the TECNIS brand of lens). These simulated results are based on a5 mm pupil diameter with no decentration (FIG. 6A) and 0.5 mmdecentration (FIG. 6B). FIG. 6A illustrates the performance for eachtype of lens when the lenses are precisely centered within the eye. InFIG. 6B, the performance of each type of lens is illustrated when thelens is decentered from the optical axis of the eye by 0.5 mm, acondition that is not uncommon under realistic conditions.

[0056] In comparing FIG. 6B to FIG. 6A, it can be seen that withdecentration, both the aspheric and multi-zonal monofocal designs suffera large loss in image quality (e.g., MTF). However, the multi-zonal lossis less compared to the aspheric design. Observe in FIG. 6A that theaspheric and multi-zonal MTFs are significantly higher compared to thestandard spherical surface design. The price paid for the significantenhancement of image quality is the sensitivity to non-nominalconditions (e.g., decentration) shown in FIG. 6B. However, someimprovement in the non-nominal condition can be achieved by this noveluse of zones in the design of an improved monofocal IOL. The price paidfor the reduction in non-nominal sensitivity is the slightly lowermulti-zonal design MTF compared to the aspheric MTF shown in FIG. 6A.Never-the-less, the multi-zonal MTF remains significantly improvedcompared to the spherical design MTF.

[0057]FIG. 7 illustrates the results of a Monte Carlo simulation in theform of plots of the average MTF performance for spherical, aspheric,and multi-zonal monofocal IOLs based on over 100 different eyes andunder varying conditions of corneal aberrations, IOL decentration, andIOL tilt. The simulation was conducted using a 5 mm nominal pupildiameter. The results compare the average performance of the varioustypes of lenses under simulated, real-world conditions.

[0058] In clinical practice, many non-nominal conditions exist. Theseinclude corneas with different aberrations, different amounts of IOLtilt and decentration, and different pupil sizes for a nominal lightingcondition. Other conditions may apply in more unique circumstances.Randomly selected values of the above “conditions” were selected,individual MTFs calculated, and the average MTF tabulated. In effect,this procedure simulates the general clinical population and assessesthe complex interaction of the IOL surface design and aberrationsinduced by the non-nominal conditions.

[0059]FIG. 7 shows the results of such a “clinical simulation”,comparing the aspheric, spherical, and multi-zonal designs. FIG. 7suggests that the aspheric design will improve the MTF at lower spatialfrequencies compared to the spherical design. From the patient'sperspective, objects will have a higher contrast and color will appearricher. FIG. 7 predicts that the multi-zonal design will provide evenmore improvement over a wide range of spatial frequencies. The patientshould experience both improved contrast and visual acuity. The latteris related to changes in MTF at about 100 cycles/mm. As expected, whenaveraged over an entire clinical population, the multi-zonal designprovides more improvement compared to an aspheric design, even thoughthe multi-zonal design is slightly lower in performance in the nominalcondition (FIG. 6a).

[0060] In certain embodiments, a method of designing a multi-zonalmonofocal IOL comprises providing an optical model of the human eye. Themodel may include a corona, an iris, the IOL 60, a retina, and anyliquids, substances, or additional devices between the these components.The model may also include various system design parameters such as thespacing between components and refractive index values.

[0061] The method further comprises providing an optical model of a lenscomprising an inner zone, an intermediate zone, an outer zone, and zonaldesign parameters (e.g., the IOL 60). The zonal design parameters foreach of the zones may include, but are not limited to, a radius ofcurvature, surface polynomial coefficients, inner radius, outer radius,refractive index, and DOE characteristics. In certain embodiments, themodel may include additional zones along with their correspondingparameters. One of the zonal design parameter may also include thenumber of zones in the lens. The model may comprise the zones and zonaldesign parameters for an anterior surface of the lens, the posteriorsurface of the lens, or both surfaces of the lens.

[0062] The method further comprises adjusting the zonal designparameters based on an image output parameter for one or morenon-optimal states of the lens. Examples of non-optimal states include,but are not limited to, IOL decentration and tilt, and different cornealaberrations (e.g., different corneal asphericities). Examples of imageoutput parameter include, but are not limited to, the ModulationTransfer Function, spot radius, and/or wavefront error. Alternatively, aplurality of output parameters may be used for evaluation whileadjusting the zonal design parameters.

[0063] With the IOL in a non-optimal state, zonal design parameters suchas the number of zones and zone radii may be adjusted to correct anyaberrant light rays entering the system entrance pupil. For example, inthe case of IOL decentration and a three-zone lens, the first zoneradius and second zone radius are chosen such that the second zone fallswithin the entrance pupil. The zonal design parameters for the zonesexposed by light entering the system entrance pupil may be adjusted tocompensate for the aberrations produced by the non-optimal state.Preferably, the zonal design parameters are adjusted until the imageoutput parameter obtains an optimized or threshold value.

[0064] The method may also include adjusting the zonal design parametersand/or the other system design parameters of the optical model based onthe image output parameter for an optimal state of the lens. Such anoptimal state would preferably represent a condition in which the IOL iscentered along the optic axis of the eye and normal thereto.

[0065] The method may be realized using optical design software that isresides on a computer or other processing device. The optical designsoftware may be used to numerically ray-traces various sets of lightrays through optical model and that evaluates the image formed on theretina. Recognizing that the modeled cornea has finite aberrations, thedesign parameters of the multi-zonal monofocal IOL may be adjusted toimprove the quality of the image formed on the retina in terms of theimage output parameter or in terms of a plurality of image outputparameters.

[0066] The resulting lens from this design may produce slightly lowerretinal image quality when placed in the optimal state as compared tothe optimal design in the optimal state. However, such a non-optimalstate design will still allow a lens to be produced that providessignificantly better performance than that possible using sphericaloptics. Thus, the non-optimal state design provides superior performanceover a greater range of non-optimal conditions as compared to theinitial optimal-design.

[0067] In certain embodiments, additional non-optimal states are used tofurther adjust the design parameters in order to provide a design thatis suitable of a particular condition or set of conditions. The resultsusing various non-optimal states may be used to provide a lens suitedfor a plurality of anticipated non-optimal states of an IOL within aneye or certain population of eyes having certain aberrations. Forinstance, the method may be used for testing the lens over a pluralityof corneal surface variations and dispositions of optical elements inthe eye's optical system using tolerance analyzing techniques.Additionally, all or part of the method may be repeated one or moretimes to modify zonal parameters and achieve a better average opticalperformance. Known algorithms, such as assigning weighting functions tothe various non-optimal states, may be used to provide a lens withdesired characteristics.

[0068] While embodiments of the invention have been disclosed for an IOLsuitable providing enhanced performance under non-optimal conditions,such as when the IOL is decentered from the optical axis of the eye,those skilled in the art will appreciate that embodiments of theinvention are suitable for other ocular devices such as contact lensesand corneal implants. For instance, the method of designing amulti-zonal monofocal IOL may be adapted for improving the performanceof contact lenses, which are known to move to different positions duringuse relative to the optical axis of the eye.

[0069] While this invention has been described with respect to variousspecific examples and embodiments, it is to be understood that these aremerely exemplary and that the invention is not limited thereto and thatit can be variously practiced within the scope of the following claims.

What is claimed is:
 1. A multi-zonal monofocal opthalmic lenscomprising: a inner zone having a first optical power; a intermediatezone surrounding the inner zone and having a second optical power thatis different from the first power by a magnitude that is less than atleast about 0.75 Diopter; and a outer zone surrounding the intermediatezone having a third optical power different from the second opticalpower.
 2. The multi-zonal monofocal opthalmic lens of claim 1, wherein,the third optical power is equal to the first optical power.
 3. Themulti-zonal monofocal opthalmic lens of claim 1, wherein the secondpower differs from the first power by a magnitude that is less than orequal to about 0.65 Diopter.
 4. The multi-zonal monofocal opthalmic lensof claim 1, wherein the inner zone comprises a spherical surface and theintermediate zone comprises an aspherical surface.
 5. The multi-zonalmonofocal opthalmic lens of claim 1, further comprising: an outer zonesurrounding the intermediate zone and having a third power wherein thesecond power differs from both the first and third powers by a magnitudethat is less than or equal to at least about 0.75 Diopter.
 6. Themulti-zonal monofocal opthalmic lens of claim 5, wherein the secondpower differs from both the first and third powers by a magnitude thatis less than or equal to about 0.65 Diopter.
 7. The multi-zonalmonofocal opthalmic lens of claim 5, wherein the inner zone comprises aspherical surface and the intermiediate zone comprises an asphericalsurface.
 8. The multi-zonal monofocal opthalmic lens of claim 7, whereinthe outer zone comprises an aspherical surface.
 9. The multi-zonalmonofocal opthalmic lens of claim 1, further comprising: multiple outerzones surrounding the intermediate zone, wherein each zone in the lenshas a power that differs from the power of the adjacent zone(s) by amagnitude that is less than or equal to at least about 0.75 Diopter. 10.The multi-zonal monofocal opthalmic lens of claim 9, wherein there arebetween 3 and 7 total zones.
 11. The multi-zonal monofocal opthalmiclens of claim 1, wherein the opthalmic lens is an intraocular lens andincludes haptics.
 12. A multi-zonal monofocal intraocular lens having anoptic with a plurality of discrete concentric optical zones centered onthe optical axis, the zones adapted to focus incoming light rays to forman image from an object, comprising: an inner zone overlapping theoptical axis of the lens for producing an image when the intraocularlens is centered on the optical axis of the human eye; and a firstsurrounding zone concentric about the inner zone and adapted tocompensate for optical aberrations in the image resulting from implantedintraocular lens decentration of greater than at least about 0.1 mm. 13.The multi-zonal monofocal intraocular lens of claim 12, wherein thefirst surrounding zone compensates for optical aberrations in the imageresulting from implanted intraocular lens decentration of greater thanabout 0.4 mm.
 14. The multi-zonal monofocal intraocular lens of claim12, wherein the first surrounding zone compensates for opticalaberrations in the image resulting from implanted intraocular lensdecentration of greater than about 0.5 mm.
 15. The multi-zonal monofocalintraocular lens of claim 12, wherein the first surrounding zone alsocompensates for optical aberrations in the image resulting fromimplanted intraocular lens tilt of greater than at least about 1 degree.16. The multi-zonal monofocal intraocular lens of claim 12, wherein thefirst surrounding zone also compensates for optical aberrations in theimage resulting from implanted intraocular lens tilt of greater than atleast about 5 degrees.
 17. The multi-zonal monofocal intraocular lens ofclaim 12, wherein the first surrounding zone also compensates foroptical aberrations in the image resulting from implanted intraocularlens tilt of greater than at least about 10 degrees.
 18. The multi-zonalmonofocal intraocular lens of claim 12, wherein the power of the firstsurrounding zone differs from the power of the inner zone by a magnitudethat is less than or equal to at least about 0.75 Diopter.
 19. Themulti-zonal monofocal intraocular lens of claim 12, wherein the innerzone comprises a spherical surface and the first surrounding zonecomprises an aspherical surface.
 20. The multi-zonal monofocalintraocular lens of claim 12, further comprising: at least one otherzone outside of the first surrounding zone, wherein each zone in thelens has a power that differs from the power of any other zone by amagnitude that is less than or equal to at least about 0.75 Diopter. 21.The multi-zonal monofocal intraocular lens of claim 20, wherein thereare between 3 and 7 total zones.
 22. A method of designing a multi-zonalmonofocal opthalmic lens, comprising: providing an optical model of thehuman eye; providing an optical model of a lens comprising an innerzone, an intermediate zone, an outer zone, and zonal design parameters;and adjusting the zonal design parameters based on an image outputparameter for one or more non-optimal states of the lens.
 23. A methodas in claim 22, further including testing the intraocular lens over aplurality of corneal surface variations and dispositions of opticalelements in the eye's optical system using tolerance analyzingtechniques.
 24. A method as in claim 22, further comprising repeating atleast a portion of the method to modify zonal parameters and achieve abetter average optical performance.